Load driving circuit and method thereof

1. A method of driving a load, the method comprising: a) monitoring an AC input to a rectifier circuit in real-time, wherein said rectifier circuit comprises first and second rectifier circuits; b) turning off a first controllable switch and turning on a second controllable switch when said AC input is in a first state, wherein said first state comprises said AC input being in a positive half cycle and increasing, or said AC input being in said positive half cycle and decreasing while being at least as high as a predetermined threshold value; c) using said AC input to supply power to a load circuit and an output capacitor via said first rectifier circuit when said AC input is in said first state, wherein said first rectifier circuit comprises a first diode and said second controllable switch; d) turning on said first and second controllable switches and using said output capacitor to supply power to said load circuit when said AC input is in a second state, wherein said second state comprises said AC input being in positive half cycle and decreasing to less than said threshold value; e) turning on said first controllable switch and turning off said second controllable switch when said AC input is in a third state, wherein said third state comprises said AC input being in a negative half cycle and having an absolute value increasing, or said AC input being in said negative half cycle and having said absolute value decreasing and at least as high as said threshold value; f) using said AC input to supply power to said load circuit and said output capacitor via said second rectifier circuit when said AC input is in said third state, wherein said second rectifier circuit comprises a second diode and said first controllable switch; and g) turning on said first and second controllable switches and using said output capacitor to supply power to said load circuit when said AC input is in a fourth state, wherein said fourth state comprises said AC input being in said negative half cycle and having an absolute value decreasing to be less than said threshold value.

2. The method of claim 1 , wherein when said AC input is in said second state, further comprising maintaining said second controllable switch as on, and turning off said first controllable switch, until said AC input enters said third state, in response to a present load driving signal being less than an expected driving signal.

3. The method of claim 2 , wherein when said AC input is in the fourth state, further comprising maintaining said first controllable switch as on, and turning off said second controllable switch until said AC input enters said first state, in response to said present load driving signal being less than said expected driving signal.

4. The method of claim 1 , wherein said threshold value comprises a voltage of about 0V.

5. The method of claim 1 , further comprising: a) determining if said load circuit is in a short-circuit state by monitoring an output voltage of said output capacitor; and b) turning off said first and second controllable switches if said load circuit is determined to be in said short-circuit state.

6. The method of claim 1 , further comprising: a) determining if said load circuit is in an open-circuit state by monitoring an output voltage of said output capacitor; and b) turning off said first and second controllable switches if said load circuit is determined to be in said open-circuit state.

7. The method of claim 1 , further comprising: a) determining if said load circuit is in an overvoltage state by monitoring said AC input in real-time; and b) turning off a fourth controllable switch if said load circuit is determined to be in said overvoltage state, wherein said fourth controllable switch is coupled between said rectifier circuit and said output capacitor.

8. The method of claim 1 , further comprising: a) turning on said second controllable switch when said AC input is in said first state and an absolute value of said AC input at a negative terminal is less than said threshold value; b) turning on a body diode of said second controllable switch when said AC input is in said first state and said absolute value of said AC input at said negative terminal is greater than said threshold value; c) turning on said first controllable switch when said AC input is in said third state and said absolute value of said AC input at a positive terminal is less than said threshold value; and d) turning on a body diode of said second controllable switch when said AC input is in said third state and said absolute value of said AC input at said positive terminal is greater than said threshold value.

9. A load driving circuit, comprising: a) an input capacitor coupled to an AC power supply and an AC input of a rectifier circuit, wherein said rectifier circuit comprises first and second rectifier circuits; b) an output capacitor coupled to said rectifier circuit and a load circuit; c) a control circuit configured to turn off a first controllable switch and turn on a second controllable switch when said AC input is in a first state, wherein said first state comprises said AC input being in a positive half cycle and increasing, or said AC input being in said positive half cycle and decreasing while being at least as high as a predetermined threshold value; d) said AC input being configured to supply power to a load circuit and an output capacitor via said first rectifier circuit when said AC input is in said first state, wherein said first rectifier circuit comprises a first diode and said second controllable switch; e) said control circuit being configured to turn on said first and second controllable switches and use said output capacitor to supply power to said load circuit when said AC input is in a second state, wherein said second state comprises said AC input being in positive half cycle and decreasing to less than said threshold value; f) said control circuit being configured to turn on said first controllable switch and turn off said second controllable switch when said AC input is in a third state, wherein said third state comprises said AC input being in a negative half cycle and having an absolute value increasing, or said AC input being in said negative half cycle and having said absolute value decreasing and at least as high as said threshold value; g) said AC input being configured to supply power to said load circuit and said output capacitor via said second rectifier circuit when said AC input is in said third state, wherein said second rectifier circuit comprises a second diode and said first controllable switch; and h) said control circuit being configured to turn on said first and second controllable switches and use said output capacitor to supply power to said load circuit when said AC input is in a fourth state, wherein said fourth state comprises said AC input being in said negative half cycle and having an absolute value decreasing to be less than said threshold value.

10. The load driving circuit of claim 9 , wherein said control circuit comprises: a) an AC input judging circuit configured to determine a state of said AC input; b) a threshold value control circuit configured to activate a comparison flip-flop signal when an absolute value of said AC input is less than said threshold value; and c) a first logic circuit coupled to said AC input judging circuit and said threshold value control circuit, wherein said first logic circuit is configured to control said first and second controllable switches according to said determined state of said AC input and said comparison flip-flop signal.

11. The load driving circuit of claim 10 , wherein said control circuit further comprises: a) a load driving feedback circuit coupled to said load circuit, and being configured to monitor said load circuit in real-time to determine a present load driving signal; b) a load feedback control circuit coupled to said load driving feedback circuit and said first logic circuit, and being configured to activate an interrupt control signal to said first logic circuit to maintain said second controllable switch as on, and to turn off said first controllable switch until said AC input enters said third state when said AC input is in said second state and if said present load driving signal is less than said predetermined driving signal; and c) said load feedback control circuit being configured to activate said interrupt control signal such that said first logic circuit maintains said first controllable switch as on, and turns off said second controllable switch until said AC input enters said first state when said AC input is in said fourth state and if said present load driving signal is less than said expected driving signal.

12. The load driving circuit of claim 10 , wherein said first logic circuit comprises: a) a flip-flop having a set terminal coupled to said threshold value control circuit to receive said comparison flip-flop signal, a reset terminal coupled to said load drive feedback control signal to receive said interrupt control signal, and an output terminal coupled to a logic sub-circuit; and b) said logic sub-circuit having a first input terminal coupled to said AC input judging circuit, an output terminal coupled to said first and second controllable switches, wherein said logic sub-circuit is configured to control said first and second controllable switches according to a state of said AC input and an output of said flip-flop.

13. The load driving circuit of claim 12 , wherein said load feedback control circuit comprises: a) a ramp generating circuit configured to turn on a third controllable switch when said AC input is in said second state or said fourth state, wherein said ramp generating circuit comprises a DC current configured to charge a charging capacitor via said third controllable switch, and said charging capacitor is configured to output a ramp voltage; b) a compensation signal generating circuit configured to generate a compensation voltage according to an error value between said load driving feedback signal and said expected voltage; and c) a fourth comparator configured to generate said interrupt control signal based on a comparison of said ramp voltage against said compensation voltage.

14. The load driving circuit of claim 10 , wherein said threshold value comprises a voltage of about 0V.

15. The load driving circuit of claim 10 , further comprising: a) a short-circuit protection circuit configured to compare an output voltage of said output capacitor against a predetermined voltage lower limit, and to generate a short-circuit protection signal; and b) a first AND-gate configured to receive an output from said short-circuit protection circuit, an output from said threshold value control circuit, and to provide a signal to a set terminal of said flip-flop.

16. The load driving circuit of claim 10 , further comprising: a) an open-circuit protection circuit configured to activate an open-circuit protection signal when an output voltage of said output capacitor is higher than a predetermined voltage upper limit; and b) a second AND-gate configured to receive said open-circuit protection signal and said interrupt control signal, and to provide a signal to a reset terminal of said flip-flop.

17. The load driving circuit of claim 10 , further comprising an input overvoltage protection circuit having: a) a fourth controllable switch coupled between said rectifier circuit and said output capacitor; and b) a fifth comparator configured to receive an AC input terminal and an input voltage upper limit, and being configured to turn off said fourth controllable switch when an absolute value of said AC input is greater than said input voltage upper limit.

18. The load driving circuit of anyone of claim 9 , wherein each of said first and second controllable switches comprises a metal-oxide-semiconductor field-effect transistor with a body diode.

19. The load driving circuit of claim 18 , wherein said control circuit comprises: a) a threshold value control circuit configured to activate a comparison flip-flop signal when an absolute value of said AC input is less than a threshold value; b) a flip-flop having a set terminal configured to receive said comparison flip-flop signal, an output terminal coupled to a second logic circuit, wherein said flip-flop is configured to generate a flip-flop signal for said logic sub-circuit; c) said second logic circuit comprising a third OR-gate configured to control said second controllable switch based on said flip-flop signal, and a comparison result between said AC input and said threshold value; and d) a fourth OR-gate configured to receive said flip-flop signal, and a comparison result between said AC input and said threshold value, and to output a signal to control said first controllable switch.